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19.5. xml.dom.minidom — Lightweight DOM implementation

xml.dom.minidom is a light-weight implementation of the Document Object
Model interface. It is intended to be simpler than the full DOM and also
significantly smaller.

DOM applications typically start by parsing some XML into a DOM. With
xml.dom.minidom, this is done through the parse functions:

fromxml.dom.minidomimportparse,parseStringdom1=parse('c:\\temp\\mydata.xml')# parse an XML file by namedatasource=open('c:\\temp\\mydata.xml')dom2=parse(datasource)# parse an open filedom3=parseString('<myxml>Some data<empty/> some more data</myxml>')

The parse() function can take either a filename or an open file object.

xml.dom.minidom.parse(filename_or_file, parser=None, bufsize=None)

Return a Document from the given input. filename_or_file may be
either a file name, or a file-like object. parser, if given, must be a SAX2
parser object. This function will change the document handler of the parser and
activate namespace support; other parser configuration (like setting an entity
resolver) must have been done in advance.

If you have XML in a string, you can use the parseString() function
instead:

xml.dom.minidom.parseString(string, parser=None)

Return a Document that represents the string. This method creates a
StringIO object for the string and passes that on to parse().

Both functions return a Document object representing the content of the
document.

What the parse() and parseString() functions do is connect an XML
parser with a “DOM builder” that can accept parse events from any SAX parser and
convert them into a DOM tree. The name of the functions are perhaps misleading,
but are easy to grasp when learning the interfaces. The parsing of the document
will be completed before these functions return; it’s simply that these
functions do not provide a parser implementation themselves.

You can also create a Document by calling a method on a “DOM
Implementation” object. You can get this object either by calling the
getDOMImplementation() function in the xml.dom package or the
xml.dom.minidom module. Using the implementation from the
xml.dom.minidom module will always return a Document instance
from the minidom implementation, while the version from xml.dom may
provide an alternate implementation (this is likely if you have the PyXML
package installed). Once you have a
Document, you can add child nodes to it to populate the DOM:

Once you have a DOM document object, you can access the parts of your XML
document through its properties and methods. These properties are defined in
the DOM specification. The main property of the document object is the
documentElement property. It gives you the main element in the XML
document: the one that holds all others. Here is an example program:

When you are finished with a DOM, you should clean it up. This is necessary
because some versions of Python do not support garbage collection of objects
that refer to each other in a cycle. Until this restriction is removed from all
versions of Python, it is safest to write your code as if cycles would not be
cleaned up.

The way to clean up a DOM is to call its unlink() method:

dom1.unlink()dom2.unlink()dom3.unlink()

unlink() is a xml.dom.minidom-specific extension to the DOM API.
After calling unlink() on a node, the node and its descendants are
essentially useless.

19.5.1. DOM Objects

The definition of the DOM API for Python is given as part of the xml.dom
module documentation. This section lists the differences between the API and
xml.dom.minidom.

Node.unlink()

Break internal references within the DOM so that it will be garbage collected on
versions of Python without cyclic GC. Even when cyclic GC is available, using
this can make large amounts of memory available sooner, so calling this on DOM
objects as soon as they are no longer needed is good practice. This only needs
to be called on the Document object, but may be called on child nodes
to discard children of that node.

Node.writexml(writer, indent="", addindent="", newl="", encoding="")

Write XML to the writer object. The writer should have a write() method
which matches that of the file object interface. The indent parameter is the
indentation of the current node. The addindent parameter is the incremental
indentation to use for subnodes of the current one. The newl parameter
specifies the string to use to terminate newlines.

For the Document node, an additional keyword argument encoding can be
used to specify the encoding field of the XML header.

Node.toxml(encoding=None)

Return the XML that the DOM represents as a string.

With no argument, the XML header does not specify an encoding, and the result is
Unicode string if the default encoding cannot represent all characters in the
document. Encoding this string in an encoding other than UTF-8 is likely
incorrect, since UTF-8 is the default encoding of XML.

With an explicit encoding[1] argument, the result is a byte string in the
specified encoding. It is recommended that this argument is always specified. To
avoid UnicodeError exceptions in case of unrepresentable text data, the
encoding argument should be specified as “utf-8”.

Node.toprettyxml(indent="", newl="", encoding="")

Return a pretty-printed version of the document. indent specifies the
indentation string and defaults to a tabulator; newl specifies the string
emitted at the end of each line and defaults to \n.

19.5.2. DOM Example

This example program is a fairly realistic example of a simple program. In this
particular case, we do not take much advantage of the flexibility of the DOM.

importxml.dom.minidomdocument="""\<slideshow><title>Demo slideshow</title><slide><title>Slide title</title><point>This is a demo</point><point>Of a program for processing slides</point></slide><slide><title>Another demo slide</title><point>It is important</point><point>To have more than</point><point>one slide</point></slide></slideshow>"""dom=xml.dom.minidom.parseString(document)defgetText(nodelist):rc=""fornodeinnodelist:ifnode.nodeType==node.TEXT_NODE:rc=rc+node.datareturnrcdefhandleSlideshow(slideshow):print("<html>")handleSlideshowTitle(slideshow.getElementsByTagName("title")[0])slides=slideshow.getElementsByTagName("slide")handleToc(slides)handleSlides(slides)print("</html>")defhandleSlides(slides):forslideinslides:handleSlide(slide)defhandleSlide(slide):handleSlideTitle(slide.getElementsByTagName("title")[0])handlePoints(slide.getElementsByTagName("point"))defhandleSlideshowTitle(title):print("<title>%s</title>"%getText(title.childNodes))defhandleSlideTitle(title):print("<h2>%s</h2>"%getText(title.childNodes))defhandlePoints(points):print("<ul>")forpointinpoints:handlePoint(point)print("</ul>")defhandlePoint(point):print("<li>%s</li>"%getText(point.childNodes))defhandleToc(slides):forslideinslides:title=slide.getElementsByTagName("title")[0]print("<p>%s</p>"%getText(title.childNodes))handleSlideshow(dom)

19.5.3. minidom and the DOM standard

The xml.dom.minidom module is essentially a DOM 1.0-compatible DOM with
some DOM 2 features (primarily namespace features).

Usage of the DOM interface in Python is straight-forward. The following mapping
rules apply:

Interfaces are accessed through instance objects. Applications should not
instantiate the classes themselves; they should use the creator functions
available on the Document object. Derived interfaces support all
operations (and attributes) from the base interfaces, plus any new operations.

Operations are used as methods. Since the DOM uses only in
parameters, the arguments are passed in normal order (from left to right).
There are no optional arguments. void operations return None.

IDL attributes map to instance attributes. For compatibility with the OMG IDL
language mapping for Python, an attribute foo can also be accessed through
accessor methods _get_foo() and _set_foo(). readonly
attributes must not be changed; this is not enforced at runtime.

The types shortint, unsignedint, unsignedlonglong, and
boolean all map to Python integer objects.

The type DOMString maps to Python strings. xml.dom.minidom supports
either bytes or strings, but will normally produce strings.
Values of type DOMString may also be None where allowed to have the IDL
null value by the DOM specification from the W3C.

const declarations map to variables in their respective scope (e.g.
xml.dom.minidom.Node.PROCESSING_INSTRUCTION_NODE); they must not be changed.

DOMException is currently not supported in xml.dom.minidom.
Instead, xml.dom.minidom uses standard Python exceptions such as
TypeError and AttributeError.

NodeList objects are implemented using Python’s built-in list type.
These objects provide the interface defined in the DOM specification, but with
earlier versions of Python they do not support the official API. They are,
however, much more “Pythonic” than the interface defined in the W3C
recommendations.

The following interfaces have no implementation in xml.dom.minidom:

DOMTimeStamp

DocumentType

DOMImplementation

CharacterData

CDATASection

Notation

Entity

EntityReference

DocumentFragment

Most of these reflect information in the XML document that is not of general
utility to most DOM users.